This invention relates to a structure of cable connection over an ground terminal, in which a coaxial cable and an ordinary cable are fixed to the ground terminal mounted, for example, on an on-vehicle antenna mounting portion, and also a braided wire of the coaxial cable is connected to the ground terminal as earth.
FIG. 3 is an exploded perspective view of a related structure of cable connection over an ground terminal used in a vehicle, and FIG. 4 is a perspective view showing the structure of FIG. 3 in its assembled condition.
The cable connection structure shown in FIGS. 3 and 4 is disclosed in Patent Literature 1 mentioned below. The ground terminal (also called “earth plate”) 1 is a terminal formed of a metal plate or a metal sheet and including a grounding plate portion 2 to be fixedly mounted on a grounding structural member (not shown) such for example as an on-vehicle antenna-mounting portion (e.g. a vehicle frame) of a vehicle. The grounding plate portion 2 has a mounting hole 2a through which it is screw fastened to the grounding structural member.
The coaxial cable 11 and an ordinary cable (power cable) 21 which are to be used at the above on-vehicle antenna mounting portion or other portion are fixed onto the ground terminal 1.
One end portion of the coaxial cable 11 to be connected to the ordinary cable 21 is beforehand subjected to an end processing operation in which a sheath 12, a braided wire 13 and an inner insulator 14 are cut off or removed over respective predetermined lengths, so that exposed portions of the braided wire 13, inner insulator 14 and inner conductor 15 are formed at the one end portion of the coaxial cable as shown in FIG. 3.
One end portion of the ordinary cable 21 to be connected to the coaxial cable 11 is beforehand subjected to an end processing operation in which a sheath 22 is cut off or removed over a predetermined length, so that an exposed portion of a core wire (conductor) 23 is formed at the one end portion of the ordinary cable 21 as shown in FIG. 3.
The exposed portion of the inner conductor 15 of the coaxial cable 11 and the exposed portion of the core wire 23 of the ordinary cable 21 are arranged in line with each other, and are press-clamped to be connected together by a crimp terminal 31.
A heat-shrinkable tube 33 of an electrically-insulative nature is fitted on the portions of the cables connected by the crimp terminal 31 and its neighboring portions for insulating purposes.
As shown in FIG. 4, the heat-shrinkable tube 33 has such a length that one end portion thereof is fitted on a distal end portion of the exposed portion of the braided wire 13 of the coaxial cable 11, while the other end portion thereof is fitted on a distal end portion of the sheath 22 at the one end portion of the ordinary cable 21.
The exposed portion of the braided wire 13 disposed at the one end portion of the coaxial cable 11 has such a length that this exposed portion, although covered at its distal end portion by the heat-shrinkable tube 33, has an uncovered portion of a predetermined length lying between the one end of the heat-shrinkable tube 33 and the sheath 12 of the coaxial cable 11 as shown in FIG. 4.
The purpose of fitting the heat-shrinkable tube 33 on the distal end portion of the braided wire 13 is to prevent the distal end portion of the braided wire 13 from becoming loose.
As shown in FIG. 3, the grounding plate portion 2 has a first sheath clamping portion 4, a second sheath clamping portion 5 and a braided wire clamping portion 6 which are formed integrally at one end edge portion thereof. The first sheath clamping portion 4 is press-fastened onto the sheath 12 of the coaxial cable 11 so as to fix the coaxial cable 11, and the second sheath clamping portion 5 is spaced from the first sheath clamping portion 4 in the direction of lengths of the cables 11 and 21, and is press-fastened onto the heat-shrinkable tube 33 fitted on the sheath 22 of the ordinary cable 21 so as to fix the ordinary cable 21, and the braided wire clamping portion 6 is disposed between the first and second clamping portions 4 and 5, and is press-fastened onto the uncovered portion of the exposed braided wire 13 so as to groundedly connect the braided wire 13 to the grounding plate portion 2.
Namely, the inner conductor 15 of the coaxial cable 11 and the core wire 23 of the ordinary cable 21 are electrically connected together by the crimp terminal 31, and with respect to the coaxial cable 11 and the ordinary wire 21 placed over the ground terminal 1, the coaxial cable 11 is fixed to the ground terminal 1 by press-fastening the first sheath clamping portion 4 onto the sheath 12 of the coaxial cable 11, and the ordinary cable 21 is fixed to the ground terminal 1 by press-fastening the second sheath clamping portion 5 onto the sheath 22 of the ordinary cable 21 through the heat-shrinkable tube 33, as shown in FIG. 4. Further, the coaxial cable 11 is groundedly connected to the ground terminal 1 by press-fastening the braided wire clamping portion 6 onto the uncovered portion of the braided wire 13 exposed adjacent to the one end of the heat-shrinkable tube 33.
[Patent Literature 1] JP-A-2007-95489
[Patent Literature 2] JP-A-2001-223040
Incidentally, generally, the inner conductor 15 of the coaxial cable 11 has a smaller thickness and a lower strength than the core wire 23 of the ordinary cable 21.
In the above cable connection structure, the inner conductor 15 of a low strength is exposed at a region indicated by A in FIG. 5, and therefore there is encountered a problem that when the inner insulator 14 and the heat-shrinkable tube 33 are expanded and contracted according to an ambient temperature change, etc., a tensile stress and a compressive stress immediately act on the inner conductor 15, so that the inner conductor 15 is liable to be damaged.
Arrows σ1 and σ2 in FIG. 5 indicate tensile stresses acting on the exposed portion of the inner conductor 15 when the inner insulator 14 and the heat-shrinkable tube 33 are contracted.